1. Field of the Invention
This invention relates to processes and equipment for preparation and cooking of edible materials. The invention relates more particularly but not exclusively to processes and equipment for the automatic slicing and deep frying of vegetables, especially potatoes.
References hereafter to "potato crisps" are to be taken as referring to relatively thin slices (typically 1-2 millimeters) of potato which have been totally immersed in suitably hot oil or otherwise cooked for sufficient time to render them not only cooked throughout, but also crisp throughout. (For the avoidance of doubt, what are known as "potato crisps" in the United Kingdom are generally called "potato chips" in the USA; however, these latter should not be confused with so-called "French-fried potatoes" which are commonly called "chips" in the United Kingdom and have a much greater thickness than crisps, together with an approximately square cross-section in contrast to the sheet-like proportions of crisps).
At present, potato crisps are commercially manufactured in the United Kingdom on a large scale by what are essentially industrial processes that cannot be scaled-down for practical adaptation to domestic circumstances. An underlying consideration in the industrial production of potato crisps is the necessity of the product having good storage properties such that the crisps can be cheaply packaged, distributed normally, and have a long shelf-life in ambient indoor conditions without perceptible degradation for a reliable minimum period of weeks or months. This consideration necessitates that the product be substantially completely dehydrated. In turn, this requires both precooking and cooking procedures that are impracticable on a domestic scale.
Thus, industrial potato crisp manufacture places the following restrictions on material and processes:
(A) Potatoes must be selected for low free sugar content (typically less than 0.25 per cent) singe higher sugar contents cause crisps to discolour at the high temperature needed (see below) due to carmelisation, which also gives an undesirable burnt taste;
(B) Potatoes have to be stored at temperatures above 9 degrees Centigrade (48 degrees Fahrenheit) singe low temperatures encourage the formation of free sugar;
(C) Potato slices must be washed and dried between slicing and cooking to remove surface starch which otherwise would cause the crisps to tend to stick together during cooking;
(D) A typical commercially sliced potato has a raw slice thickness of about 1.55 millimeters which can result in a tendency to ballooning during cooking, in which opposite sides of localized areas of the slice separate due to steam bubbles forming between them; this diminishes the quality of the product; and
(E) Cooking is undertaken by immersing the potato slices for a period of about four minutes in oil at a temperature of at least 185 degrees Centigrade (365 degrees Fahrenheit); cooking time must be carefully controlled to achieve thorough dehydration without burning while the high temperature increases the risk of over-cooking/burning and in any event, the heat produces large quantities of malodorous hot oil vapour that would be unacceptable in a domestic environment.
In comparison to the rigorous industrial requirements, the domestic production of potato crisps should ideally meet the following criteria:
(1) Any type of potato that is ordinarily available to the domestic user should be capable of being used (and regardless of its storage conditions); i.e. free sugar content should be immaterial (with the possible limitation that slices of raw potato should be coherent and not disintegrate);
(2) Slicing should be mechanised to produce uniform slices without laborious and skilled handling of a knife;
(3) Washing and drying of potato slices should be eliminated as being particularly laborious and time-consuming if not performed by (necessarily complex) machinery;
(4) Cooking temperature should be reduced to minimise and preferably eliminate the risk of burning the crisps, and to minimise oil fumes; and
(5) Despite the desirably reduced cooking temperature, cooking time is preferably also reduced to minimise perceived delays and avoid consumer impatience, but simultaneously, the cooking time should not be so critical as cause problems in quality control due to timing errors; for example, optimum cooking time may vary according to the variety of the potato being used, but the cook may be unappreciative of such varietal differences, or unable to ascertain the differences. Also, if a crisp or a fragment of a crisp fails to be removed from the cooking oil at the conclusion of the cooking cycle so as to be subjected to a second cooking cycle, this should not burn the doubly-cooked crisp (or fragment) and preferably should not even render the crisp inedible. Preferably, prolonged or even indefinitely long cooking should not degrade the crisps.
2. Description of the Related Art
It is known to provide domestic cooking equipment in the form of externally or internally heated pans filled with oil and fitted with detachable wire baskets to withdraw cooked food. Such equipment is commonly employed to fry relatively thick strips of potato to produce "chips" (in the United Kingdom usage; "French fries" in the American usage). At most, only a relatively thin crust of such chips is crisp when normally cooked. However, such equipment is unsuitable for the domestic production of potato crisps, singe the thin raw potato slices must either be individually washed and dried, or separately loaded in succession into the pan to avoid adhering to one another, which readily leads to unequal cooking times. Moreover, after a few seconds, the semi-raw slice rises to the surface where it cooks on one side only if left untended. Forced submersion or constant turning is necessary to ensure even cooking of both sides. Thus the known equipment is unsuited to semi-automatic or fully automatic cooking of potato crisps. A proposal has been made in U.S. Pat. No. 3,280,723 for a machine to slice, fry, and dispense potato crisps. The basis of this prior machine is a large trough of oil forming an endless loop in a "racetrack" configuration. Hot oil is forcibly circulated to flow around the loop in a continuous stream. A potato slicer is intermittently operated to drop slices of raw potato into the oil stream, where they are carried along in a random manner. Throughout most of the cooking process, the position of any given slice is uncontrolled. After some indeterminate lapse of time, the fried potato slices are discharged from the end of the machine. The machine is said to deliver a measured quantity of potato crisps, but in fact the quantity is set by starting and stopping what is essentially a continuous process. In contrast to the present invention, the prior machine is not a batch cooker. The prior machine entirely lacks the continuous positive control of slice position that is an important feature of the present invention from beginning to end of the slicing and cooking process. Moreover, the prior machine is a floor-mounted machine which is very much larger and heavier than any practicable domestic crisp maker; the prior machine is a commercial system designed for use in a "fast food" shop and is quite different from the present invention which is specifically designed for use on a kitchen work top or in other convenient domestic locations.
It is therefore an object of the invention to provide preparation and cooking procedures and equipment which obviate or mitigate the above-described disadvantages. While the primary object of the invention is to provide procedures and equipment particularly suited to the domestic production of potato crisps, it is also an object of the invention to provide procedures and equipment which are suitable per se, or with adaptation or modification (such as, for example by production of slices of different thickness) to the preparation and cooking of other edible materials, such as vegetables other than potatoes, fruits, and doughs. In the latter case, a ready-mixed but uncooked dough may be rolled or otherwise formed into a thin sheet whose thickness is suitable for cooking to form crisps without further preliminary reduction in thickness; in such a case, regular or irregular pieces of suitable size can be cut prior to cooking and fed to the equipment, in which case a slicing mechanism or its functional equivalent in the equipment can be bypassed, or partially or totally removed from the equipment, or omitted from the equipment as built and supplied to the user. Suitable dough mixtures may be based on flour formed from wheat, maize, manioc, or other edible farinaceous substances (or mixtures of these) and may incorporate flavouring and/or colouring. Crisp-like edible products formed from such dough mixtures are industrially manufactured and commercially sold in competition with traditional potato crisps.
References in this specification to "edible materials" include not only materials which are edible when uncooked, but also include materials which may be unpalatable or inedible when uncooked but become edible when prepared and cooked to form crisp-like products. The crisps or crisp-like products formed by the procedures and equipment of the invention may or may not have significant nutritional value, being generally in the form of a savoury confectionery.